WO2011074171A1

WO2011074171A1 - Defect inspection apparatus and defect inspection method

Info

Publication number: WO2011074171A1
Application number: PCT/JP2010/006479
Authority: WO
Inventors: 昌昭伊東
Original assignee: 株式会社日立ハイテクノロジーズ
Priority date: 2009-12-14
Filing date: 2010-11-04
Publication date: 2011-06-23
Also published as: US20120327415A1; JP2011122990A

Abstract

Disclosed is a defect inspection apparatus having a high sensitivity and a high throughput, in defect inspection of a sample having a pattern of a semiconductor wafer and the like formed thereon. The defect inspection apparatus is characterized by the direction of the pattern, the direction of the projection of illuminating light to the sample, and polarization of the illuminating light. The projections to the sample in at least two illuminating directions are perpendicular or parallel to the direction of the major pattern of the sample, and the polarization light of the illuminating light in the first direction and the polarization light of the illuminating light in the second direction are different from each other. The projection in the first direction and the projection in the second direction are either perpendicular to each other or parallel to each other. The polarization light of the illuminating light in the first direction is s-polarization light, and the polarization light of the illuminating light in the second direction is p-polarization light.

Description

Defect inspection apparatus and defect inspection method

The present invention relates to a defect inspection apparatus and a defect inspection method for a sample on which a pattern is formed such as a wafer in semiconductor device manufacture, and more particularly to an optical system in an optical defect inspection apparatus.

In the semiconductor device manufacturing process, film formation by sputtering or chemical vapor deposition, planarization by chemical mechanical polishing, and patterning by lithography and etching are repeated many times. In order to secure the yield of the semiconductor devices, the wafer is removed in the middle of the manufacturing process and defect inspection is performed. The defects are foreign matter, swelling, voids, scratches, and pattern defects (short, open, hole opening defects, etc.) on the wafer surface. The purpose of the defect inspection is, firstly, to manage the state of the manufacturing apparatus, and secondly, to identify the process in which the defect has occurred and its cause. With the miniaturization of semiconductor devices, high detection sensitivity is required of the defect inspection apparatus.

Hundreds of devices (called chips) having the same pattern are fabricated on the wafer. In addition, in the memory unit of the device, a large number of cells having a repetitive pattern are formed. In the defect inspection apparatus, a method of comparing images between adjacent chips or adjacent cells is used.

A dark field defect inspection apparatus that irradiates light to a wafer to compare dark field images is often used in in-line inspection because the throughput is higher than that of the other type of defect inspection apparatus.

Japanese Patent Laid-Open No. 2005-156537 (Patent Document 1) is disclosed as to a dark field defect inspection apparatus. Illumination light is irradiated to the wafer from a plurality of directions, and scattered light from the wafer is detected for each direction. For each illumination direction, the incident angle of the illumination light is different, and the wavelength of the illumination light is the same or different.

Further, Japanese Patent Application Laid-Open No. 2007-225432 (Patent Document 2) is disclosed regarding a dark field defect inspection apparatus. Illumination light is irradiated to the wafer from a plurality of directions, and scattered light from the wafer is detected for each direction. The polarization of the illumination light is different for each illumination direction.

JP, 2005-156537, A Unexamined-Japanese-Patent No. 2007-225432

With the miniaturization of semiconductor devices, it is required to improve the detection sensitivity of the optical defect inspection apparatus. In particular, in inspection after patterning of gates, bit lines, etc., it is necessary to detect very short shorts and opens, and securing of signal strength is a problem.

The technique of Patent Document 1 reduces speckle noise from pattern edges by integrating images in a plurality of directions. However, the signal strength is not considered.

The technique of Patent Document 2 stabilizes the signal intensity against the thickness variation of the oxide film by the illumination light whose polarization is different from each other. However, the target defects are foreign substances, and no consideration is given to pattern defects.

An object of the present invention is to provide a high sensitivity and high throughput defect inspection apparatus, in particular for pattern defects.

In order to achieve the above object, the feature of the present invention is to focus on the direction of the pattern, the direction of projection of the illumination light onto the sample, and the polarization of the illumination light.

Further, the present invention irradiates illumination light from a plurality of directions to a sample on which a pattern is formed, forms an image of the sample through an optical system on an image sensor, and determines the presence or absence of a defect. In which the projection of at least two illumination directions onto the sample is perpendicular or parallel to the direction of the main pattern of the sample, the polarization of the illumination light in the first direction and the illumination light in the second direction Are characterized in that they are different from each other.

Also, the invention is characterized in that the projection of the first direction and the projection of the second direction are perpendicular to each other.

Furthermore, the invention is characterized in that the projection of the first direction and the projection of the second direction are parallel to each other.

The present invention is further characterized in that the polarization of the illumination light in the first direction is s-polarization, and the polarization of the illumination light in the second direction is p-polarization.

Further, the present invention is characterized in that the optical system is a dark field type.

Further, the present invention is characterized in that the optical system is a bright field type.

Further, the present invention is characterized in that the illumination light in the first direction and the illumination light in the second direction are spatially incoherent.

Furthermore, the present invention is characterized in that the illumination light in the first direction and the illumination light in the second direction are spatially coherent.

Furthermore, the present invention irradiates illumination light from a plurality of directions to a sample on which a pattern is formed, and forms an image of the sample through an optical system on an image sensor to determine the presence or absence of a defect. Wherein the projection of at least two illumination directions onto the sample is perpendicular or parallel to the direction of the main pattern of the sample, and the wavelength of the illumination light in the first direction and the illumination light in the second direction The first and second directions are different from each other, and the polarization of the illumination light in the first direction and the polarization of the illumination light in the second direction are different from each other.

According to the present invention, a highly sensitive and high-throughput defect inspection can be performed by an illumination method suitable for detecting a short or an open.

It is a figure which shows 1st Embodiment of the defect inspection apparatus which concerns on this invention. It is a figure which shows the relationship between the pattern in a wafer, and illumination light. It is a figure which shows the relationship between illumination conditions and the signal strength of a short. FIG. 7 shows two-way illumination for shorts. It is a figure which shows 4 direction illumination with respect to short. It is a figure which shows the relationship between illumination conditions and the signal strength of open. FIG. 7 shows two-way illumination for short and open. FIG. 7 illustrates another two-way illumination for short and open. It is a figure which shows the flow of illumination condition setting. It is a figure which shows the operation screen of lighting condition setting. It is a figure which shows 2nd Embodiment of the defect inspection apparatus which concerns on this invention. In 2nd Embodiment, it is a figure which shows 2 direction illumination with respect to short. It is a figure which shows the relationship between an oxide film thickness and the signal strength of a short.

As one embodiment of the present invention, a dark field defect inspection apparatus for a semiconductor wafer will be described.

A schematic configuration of the inspection apparatus is shown in FIG. The inspection apparatus includes a stage 2 on which the wafer 1 is mounted, a light source 3, a branching element 4, a first polarizing element 51, a second polarizing element 52, a first illumination optical system 61, a second illumination optical system 62, and detection. It comprises an optical system 7, a detector 8, an image processing unit 9, an overall control unit 10, and an input / output operation unit 11.

When loading the wafer 1 into the defect inspection apparatus, the operator inputs information such as a pattern layout and a target defect type into the input / output operation unit 11. The overall control unit 10 uses this information to select a suitable illumination method as described later.

The light emitted from the light source 3 is split into two light paths by the branching element 4. The respective light beams become two linearly polarized lights orthogonal to each other by the

polarizing elements

51 and 52, and illuminate the wafer 1 through the illumination

optical systems

61 and 62. The first illumination light and the second illumination light are spatially incoherent because the optical path lengths are different from each other. The direction of the first illumination light and the direction of the second illumination light are set so that the projections on the wafer surface are perpendicular to each other. Here, projection means the component in the wafer surface of the direction vector of illumination light. The projection is perpendicular or parallel to the main pattern of the wafer. Further, with respect to the wafer, the first illumination light is s-polarized light, and the second illumination light is p-polarized light. The light scattered by the wafer is collected by the detection optical system 7. Since the specularly reflected light from the wafer is emitted out of the aperture of the detection optical system, a dark field image is formed on the detector 8. The inspection image is converted into a digital signal by an A / D converter (not shown) and recorded in the image processing unit 9. In the image processing unit, a reference image which is adjacent to the inspection chip and acquired by a chip having the same pattern is recorded. After processing such as alignment is performed on the inspection image and the reference image, a difference image of the both is output. The luminance of this difference image is compared with a preset threshold value to determine the presence or absence of a defect. The determination result of the defect is transmitted to the overall control unit, and displayed on the input / output operation unit after completion of the predetermined inspection.

FIG. 2 shows the relationship between the pattern in the embodiment and the illumination light. A line and space pattern is formed on the wafer, and illumination light is irradiated from two directions. The projection of the first direction onto the wafer is perpendicular to the pattern pitch direction. The projection of the second direction onto the wafer is parallel to the pattern pitch direction. Thus, the projection of the first direction and the projection of the second direction are perpendicular to one another. With regard to polarization, the illumination light in the first direction is s-polarization, and the illumination light in the second direction is p-polarization.

In the present invention, the direction and polarization of the illumination light are set according to the pattern and the defect of interest. Details will be described below.

In pattern defect inspection, detection of a short, which is a fatal defect, is particularly important. FIG. 3 shows the relationship between the azimuth angle of the illumination light and the signal strength for the short circuit of the line and space pattern. Here, the azimuth is defined as the angle between the projection of the illumination direction onto the wafer and the pattern pitch direction. It can be seen that the signal strength is dependent on polarization and azimuth. The short signal strength is maximum at an azimuth angle of 90 degrees for s-polarization and at an azimuth angle of 0 degrees for p-polarization. In either case, the projection of the electric field vector of the illumination light onto the wafer is parallel to the pattern pitch direction. On the other hand, when the azimuth angle is 0 degree for s-polarization and 90 degrees for p-polarization, the short signal strength is zero.

By the way, when the illumination light is irradiated to the wafer from one direction, speckle is easily generated due to the grain of the wafer surface or the roughness of the line edge, which often hinders the defect detection. In order to reduce such noise, it is effective to emit illumination light from a plurality of directions to reduce spatial coherence.

In consideration of the above, an illumination method suitable for irradiating a wafer with illumination light from two directions and detecting a pattern short is shown in FIG. Illumination light of s-polarization is emitted from a direction perpendicular to the pattern pitch direction, and illumination light of p-polarization is emitted from a direction parallel to the pattern pitch direction. Such two-directional illumination can ensure short signal strength while reducing noise.

Further, an illumination method suitable for irradiating the wafer with illumination light from four directions and detecting a pattern short is shown in FIG. Illumination light of s-polarization is emitted from two directions perpendicular to the pattern pitch direction, and illumination light of p-polarization is emitted from two directions parallel to the pattern pitch direction. Although the four-directional illumination complicates the illumination optical system compared to the two-directional illumination described above, noise can be further reduced.

Moreover, in pattern defect inspection, detection of an open which is a fatal defect is also important. FIG. 6 shows the relationship between the azimuth angle of the illumination light and the signal strength with respect to the opening of the line and space pattern. The open signal strength is maximized at p-polarization at an azimuth of 90 degrees. However, under this condition, as shown in FIG. 3, the short signal strength becomes zero.

Therefore, a suitable illumination method for detecting both shorts and open wafers is shown in FIG. Illumination light is applied to the wafer from two directions perpendicular to the pattern pitch direction. The first illumination light is s-polarized, and the second illumination light is p-polarized. With such two-directional illumination, a short can be detected by the first illumination light, and an open can be detected by the second illumination light.

Also, another illumination method suitable for detecting both short and open is shown in FIG. Illumination light is applied to the wafer from two directions parallel to the pattern pitch direction. The first illumination light is s-polarized, and the second illumination light is p-polarized. With such two-directional illumination, the open can be detected by the first illumination light, and the short can be detected by the second illumination light.

A flow of setting by the user regarding the illumination conditions described above is shown in FIG. First, the main direction of the pattern on the inspection apparatus is input at the input / output operation unit. Next, the target defect type is input. Based on the above input information, the overall control unit selects a recommended illumination condition and displays it on the operation screen. The user confirms this lighting condition and sets and registers it in the inspection recipe. FIG. 10 shows the operation screen in the case where the pattern direction is the Y direction, the defect type of interest is the short, and the illumination light direction is the two directions.

Next, inspection of pattern defects on the oxide film will be described. Since the oxide film is transparent, thin film interference occurs, and the signal strength varies significantly depending on the oxide film thickness. For a wafer with large film thickness unevenness, a method of illuminating with light of different wavelengths is effective to reduce the thin film interference effect.

A second embodiment of the present invention suitable for pattern defect inspection on an oxide film will be described with reference to FIG. The light source 31 emits far ultraviolet light, and the light source 32 emits ultraviolet light. The far ultraviolet light irradiates the wafer with linearly polarized light via the first polarizing element 51 and the first illumination optical system 61. The ultraviolet light illuminates the wafer with linearly polarized light through the second polarizing element 52 and the second illumination optical system 62. Here, the direction of the far ultraviolet light and the direction of the ultraviolet light are set so that the projections on the wafer surface are perpendicular to each other. The projection is perpendicular or parallel to the main pattern of the wafer. Also, the polarization of far ultraviolet light and the polarization of ultraviolet light are different, one is s-polarization and the other is p-polarization. The far ultraviolet light and the ultraviolet light scattered by the wafer are collected by the detection optical system 7, and a dark field image is formed on the detector 8.

An illumination method suitable for detecting pattern shorts is shown in FIG. The s-polarized far-ultraviolet light is irradiated from a direction perpendicular to the pattern pitch direction. The p-polarized ultraviolet light is irradiated from a direction parallel to the pattern pitch direction.

FIG. 13 shows the relationship between the oxide film thickness and the signal strength of the short. It can be seen that the signal intensity of the far ultraviolet light and the signal intensity of the ultraviolet light significantly change with respect to the film thickness. On the other hand, the sum of the signal intensity of far ultraviolet light and the signal intensity of ultraviolet light has a small fluctuation with respect to the film thickness. As described above, two-directional illumination with different wavelengths and polarizations can ensure signal strength even on wafers with uneven film thickness.

In the above embodiments, the illumination light is spatially incoherent, but the optical path lengths can be made identical to make it coherent. In coherent illumination, although noise increases, interference effects may further increase the signal strength. Therefore, although the noise is sufficiently small, it is effective when the signal strength is insufficient.

Also, in the above embodiments, the projection of the illumination direction onto the wafer surface is perpendicular or parallel to the main direction of the pattern, but substantially the same effect can be obtained even if the angle deviates a little.

Also, in the above embodiments, the polarization of the illumination light is s-polarization and p-polarization, but even if the polarization is somewhat offset, substantially the same effect can be obtained.

Also, in the above embodiments, the illumination area on the wafer can be slit. By scanning the wafer in the lateral direction, high throughput defect inspection is possible.

Further, in the above embodiments, a plurality of detection systems can be provided. In many cases, the scattered light distribution of defects changes with the oxide film thickness. Therefore, the combined use of the upper detection system and the oblique detection system provides the effect of stabilizing the detection sensitivity to film thickness unevenness.

Moreover, although the dark-field defect inspection apparatus of a semiconductor wafer was demonstrated in the above embodiment, this invention is applicable also to a bright-field defect inspection apparatus.

The present invention is also applicable to inspection of a sample on which a fine pattern such as a mask in a semiconductor lithography process is formed.

DESCRIPTION OF SYMBOLS 1 wafer 2 stage 3 light source 4 branch element 7 detection optical system 8 detector 9 image processing unit 10 overall control unit 11 input / output operation unit 51 first polarization element 52 second polarization element 61 first illumination optical system 62 first 2 illumination optics

Claims

In a defect inspection apparatus, a sample on which a pattern is formed is irradiated with illumination light from a plurality of directions, an image of the sample is formed on an image sensor through an optical system, and the presence or absence of a defect is determined.
The projection of the at least two illumination directions onto the sample is perpendicular or parallel to the direction of the pattern of the sample,
A defect inspection apparatus, wherein the polarization of the illumination light in the first direction and the polarization of the illumination light in the second direction are different from each other.
In the defect inspection apparatus according to claim 1,
A defect inspection apparatus, wherein the projection of the first direction and the projection of the second direction are perpendicular to each other.
In the defect inspection apparatus according to claim 1,
A defect inspection apparatus, wherein the projection of the first direction and the projection of the second direction are parallel to each other.
In the defect inspection apparatus according to claim 1,
The defect inspection apparatus, wherein the polarization of the illumination light in the first direction is s-polarization, and the polarization of the illumination light in the second direction is p-polarization.
In the defect inspection apparatus according to claim 1,
The defect inspection apparatus characterized in that the optical system is a dark field type.
In the defect inspection apparatus according to claim 1,
The defect inspection apparatus characterized in that the optical system is a bright field type.
In the defect inspection apparatus according to claim 1,
A defect inspection apparatus, wherein the illumination light in the first direction and the illumination light in the second direction are spatially incoherent.
In the defect inspection apparatus according to claim 1,
A defect inspection apparatus, wherein the illumination light in the first direction and the illumination light in the second direction are spatially coherent.
In a defect inspection apparatus, a sample on which a pattern is formed is irradiated with illumination light from a plurality of directions, an image of the sample is formed on an image sensor through an optical system, and the presence or absence of a defect is determined.
The projection of the at least two illumination directions onto the sample is perpendicular or parallel to the direction of the pattern of the sample,
The wavelength of the illumination light in the first direction and the wavelength of the illumination light in the second direction are different from each other
A defect inspection apparatus, wherein the polarization of the illumination light in the first direction and the polarization of the illumination light in the second direction are different from each other.
In the defect inspection apparatus according to claim 9,
A defect inspection apparatus, wherein the projection of the first direction and the projection of the second direction are perpendicular to each other.
In the defect inspection apparatus according to claim 9,
A defect inspection apparatus, wherein the projection of the first direction and the projection of the second direction are parallel to each other.
In the defect inspection apparatus according to claim 9,
The defect inspection apparatus, wherein the polarization of the illumination light in the first direction is s-polarization, and the polarization of the illumination light in the second direction is p-polarization.
In the defect inspection apparatus according to claim 9,
The defect inspection apparatus characterized in that the optical system is a dark field type.
In the defect inspection apparatus according to claim 9,
The defect inspection apparatus characterized in that the optical system is a bright field type.
In the defect inspection apparatus according to claim 9,
A defect inspection apparatus, wherein the illumination light in the first direction and the second illumination light are spatially incoherent.
In the defect inspection apparatus according to claim 9,
A defect inspection apparatus, wherein the illumination light in the first direction and the second illumination light are spatially coherent.
In the defect inspection system
A stage for moving the pattern-formed sample;
A first illumination optical system for irradiating the sample with a first light;
A second illumination optical system that emits a second light of a polarization state different from the first light;
A detection optical system that detects light from the sample;
A processing unit that determines the presence or absence of a defect using the detection result of the detection optical system;
A defect inspection apparatus, wherein the projection of the first light onto the sample and the projection of the second light onto the sample are different in direction from each other.
In the defect inspection apparatus according to claim 17,
The projection of the first light onto the sample is perpendicular to the pattern pitch of the sample, and the projection of the second light onto the sample is parallel to the pattern pitch of the sample Defect inspection device.
It is a defect inspection method of the sample in which the pattern was formed, and
Irradiating the sample with at least two or more lights of different polarization states;
The defect inspection method characterized in that the projections of the two lights onto the sample are different in direction from each other.